This invention relates generally to a hydraulic circuit for controlling the elevational position of a bulldozer blade or the like, and more particularly, to the incorporation and control of a quick drop valve for improving the efficiency of the circuit.
Quick drop valves are commonly used in hydraulic control circuits for bulldozer blades or the like in which the blade is allowed to free-fall to ground level under the force of gravity. Some of the fluid expelled from the hydraulic cylinders which control blade elevation is diverted by the quick drop valves to the expanding ends of the hydraulic cylinders to supplement the pump flow thereto. Without any type of quick drop valve, the expanding ends of the hydraulic cylinders may cavitate quite significantly. Since the cavitated ends of the cylinders have to be filled with fluid from the pump after the blade comes to rest on the ground, a considerable time lag occurs before sufficient downward force can be applied to the blade for penetrating the ground. The use of quick drop valves minimizes the cavitation and thus reduces the time lag.
The duration of the time lag depends upon the efficiency of the quick drop valve, which is determined by the amount of expelled fluid that the quick drop valve diverts back to the expanding side of the cylinders. That amount is dependent upon how quickly the quick drop valve moves to the quick drop position in a free-fall situation and the percentage of the expelled fluid that the quick drop valve diverts back to the expanding ends once it is in the quick drop position.
An example of a quick drop circuit is provided by U.S. Pat. No. 5,014,734 to Smith which provides a hydraulic circuit having a quick drop valve that is actuated based on the pressures created by the hydraulic fluid flow through the circuit. Actuation of the quick drop valve occurs somewhere within a range of movement of an operator controlled lever during a controlled lowering operation which may be non-intuitive to the operator. Further, the operation controlled lever lacks a position for a floating blade operation to allow the blade to freely move vertically when traveling along the surface of the ground.
The present invention is directed to overcoming one or more of the problems as set forth above.
In accordance with one aspect of the invention, a fluid circuit for raising and lowering an implement includes a quick drop valve member movable between at least a first position and a second position, the first position corresponding to a non-quick drop hydraulic fluid flow path of the fluid circuit and the second position corresponding to a quick drop hydraulic fluid flow path of the fluid circuit, the quick drop valve member being movable between at least the first and second positions based on pressures in the fluid circuit produced by hydraulic fluid. The fluid circuit further including a control system configured to selectively apply a biasing force against the quick drop valve member biasing the quick drop valve in the first position, the control system providing the biasing force independent of pressures in the fluid circuit produced by the hydraulic fluid.
According to another aspect of the present invention, a fluid circuit for raising and lowering an implement includes a hydraulic fluid pump, at least one hydraulic cylinder selectively hydraulically coupled to the hydraulic fluid pump, the at least one hydraulic cylinder including a lift side and a drop side and being coupled to a working implement, at least one control valve located between the hydraulic fluid pump and the at least one hydraulic cylinder, a hydraulic-fluid-actuated quick drop valve located between the control valve and the at least one hydraulic cylinder, the quick drop valve including a quick drop valve member movable between a first valve member position blocking hydraulic fluid communication between the lift side and drop side of the at least one hydraulic cylinder, and a second valve member position allowing hydraulic fluid communication between the lift side and the drop side of the at least one hydraulic cylinder, and a fluid lock selectively fluidly biasing the quick drop valve member in the first position.
According to another aspect of the present invention, a fluid circuit for raising and lowering an implement includes a hydraulic fluid pump, a plurality of hydraulic cylinders selectively hydraulically coupled to the hydraulic fluid pump, the plurality of hydraulic cylinders each including a lift side and a drop side and being coupled to a working implement, at least one control valve located between the hydraulic fluid pump and the plurality of hydraulic cylinders, the control valve having four positions, the four positions corresponding to a rising implement operation of the fluid circuit, a controlled lowering of implement operation of the fluid circuit, a holding of implement operation of the fluid circuit and a floating of implement operation of the fluid circuit, a quick drop valve located between the control valve and the plurality of hydraulic cylinders, the quick drop valve including a quick drop valve member movable by hydraulic fluid within the fluid circuit between a first valve member position blocking hydraulic fluid communication between the lift sides and drop sides of the plurality of hydraulic cylinders and a second valve member position allowing hydraulic fluid communication between the lift sides and the drop sides of the plurality of hydraulic cylinders, and a solenoid valve having a flow-through position allowing pressurized pilot fluid to flow to the quick drop valve to bias the quick drop valve member in the first position, and a blocked position disconnecting the pressurized pilot fluid flow to the quick drop valve member, the solenoid valve being actuated to its blocked position by an electric switch activated by moving an operator controlled lever to a triggering position.
According to yet another aspect of the present invention, a method for controlling movement of an implement includes positioning an operator controlled lever to at least a first position corresponding to a raising implement operation and the application of a biasing force against a quick drop valve member of a quick drop valve, positioning the operator controlled lever to at least a second position corresponding to a holding implement operation and the application of the biasing force against the quick drop valve member, positioning the operator controlled lever to at least a third position corresponding to a controlled lowering implement operation and the application of the biasing force against the quick drop valve member, and positioning the operator controlled lever to at least a fourth position corresponding to a releasing of said biasing force against the quick drop valve member to allow the quick drop valve member to move between a quick drop position and a non-quick drop position.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an exemplary embodiment of the invention and together with the description, serve to explain the principles of the invention.